An angel appears in Tom's dream in the form of a savior who releases the chimney sweepers from their coffins, and tells Tom that if he's a good boy God will love him. It seems like the angel is telling Tom to do his job. Does that mean that, in "The Chimney Sweeper," religion, in a way, participates in the exploitation of children? In a word, yes. Blake uses Tom Dacre's sad, beautiful dream to demonstrate how these boys' religious beliefs keep them contained in their dreadful lifestyle, rather than allow them to rise above it.
"The Chimney Sweeper" suggests that religion sometimes contributes to child suffering, because the angel straight up tells Tom to work hard at his awful job so he can earn God's love. Does that sound fair to you?
The most important religious moment—the angel unlocking the coffins—happens in a dream, which tells us that there's something unreal or totally fantastical about these boys' religious beliefs.